An expressive style of anger regulation (anger-out) is related to increased sensitivity to acute and chronic pain. Based on the role of endogenous opioids in modulation of pain, stress responsiveness, and emotional state, it was hypothesized that anger-out may exert its effects on chronic and acute pain via dysfunction in endogenous opioid systems. Preliminary data support this hypothesis with regard to dispositional anger-out. However, recent finding indicate that behavioral anger expression when anger is aroused may be analgesic in high anger-outs, suggesting that examination of Trait X State interactions could be crucial for understanding mediators of anger-out's health effects. The role of opioids in expression of these interactions is unknown. The specific aims of the proposed study are: 1) determine whether behavioral anger expression in high anger-outs triggers opioid-mediated analgesia, and 2) determine the relationships between opioid- related effects of anger-out, in vivo behavioral anger expression, and daily chronic pain variables. Exploration of the clinically important phenomenon of anger expression as it impacts on endogenous opioid pain regulatory system function will improve understanding of the psychobiological relationships that may contribute to both acute and chronic pain responsiveness. One hundred forty subjects with chronic low back pain and 80 pain-free healthy subjects will participate in two laboratory sessions, once under opioid blockade with naloxone and once under placebo. Subjects will undergo either an anger recall interview to elicit anger arousal and behavioral anger expression, or a control non anger-arousing interview. Next, subjects will undergo acute finger pressure pain and ischemic pain stimuli. Subjects will also complete a daily electronic pain and behavioral anger expression diary between laboratory sessions. Results will reveal whether verbal anger expression when anger is aroused triggers opioid analgesia in high anger-out individuals. If the known positive relationship between chronic pain intensity and anger-out is mediated by absolute opioid dysfunction, statistical control of opioid blockade responses to acute pain (index of opioid analgesic function) should eliminate this relationship. However, if the apparent opioid dysfunction in high anger-outs is ameliorated by behavioral anger expression in the lab, the effects of opioid triggering on chronic pain in response to in vivo behavioral anger expression should be evident in intensive diary data.